introduced 1947 (at 14th conference of the Union Internationale de Chimie) as a prefix for units of one thousand-millionth part, from Greek nanos "a dwarf." According to Watkins, this is originally "little old man," from nannos "uncle," masc. of nanna "aunt" (see nana). Earlier it was used as a prefix to mean "dwarf, dwarfish," and still in a non-scientific sense of "very small."

/nan'oh/ 1. A prefix meaning 10^-9 or one billionth. Used loosely to mean "small", e.g. nanotechnology, or (rarely), following "nanosecond", to mean a short time, e.g. "I'll be with you in a nano". [Jargon File] (2002-03-02)